Quote:
Originally Posted by Oggie
Please excuse my ignorance, how will pressure testing locate the issue (genuine question)?
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A good shop should be able to determine not only if the cooling system is leaking but where it is most likely leaking from.
For example, they can pressurize the cooling system and monitor cylinder pressure at the same time - if the cyl pressure shows an increase, then the head is likely cracked in that cylinder. This isn't an exact test (in psi), its just an indicator of what might be going on inside the engine.
In your case (where you haven't yet replaced the oil cooler), they can easily figure out if that is the source of the leak (they will hear the pressurized air coming out of the top of the engine where the oil cooler mounts).
A good shop knows all of these kinds of troubleshooting techniques and has the experience and equipment to perform them since that is what they do for a living - and that is why they are worth $150/hour.
Now, it is definitely possible that they can't find the leak (and you might feel as if you wasted your money) but as I said, its worth a couple hundred bucks to see what they might turn up before starting a tear down.
I had my local shop do this test on my Boxster when I was losing coolant but had no obvious leaks and no intermix - where is it going? They found that I likely had a leak into a cyl and a subsequent leak down test on the cylinders confirmed it (coolant was leaking into a cylinder and going out the exhaust).